Posted by Todd Wilson on Friday, April 02, 2004 at 1:54AM :
In Reply to: 1975 W-100 symptom posted by Jim Crane on Thursday, April 01, 2004 at 5:22PM :
I would suspect a vacuum leak somewhere. Could be in the power brake booster or in the carb area. The 2 barrel carbs are famous for wearing on the shafts causing a leak. I have had no luck in ever rebuilding a 2 barrel carb. A loose timing chain will cause the timing to jump up and down with rpms. If it jumps teeth it will backfire and run like crap in general before it gives up the ghost.
If you have no ping 38 degrees total advance on the timing at least 2000rpms. You can adjust the idle screws with a vacuum gauge to get the best adjustment. Need to get the highest vacuum also. You can use the vacuum gauge to adjust timing also.
Due to your good PSI of the cylinders probably not a worn cam shaft and the rings are good.
Your 75 has electonic ignition and not points so that rules out a points problem. ECU boxes either work or they dont.
It might be a ballast resistor.Generally they work or dont work but I did have a nasty idle hesitation on my 74 440 a few years ago and it was a bad ballast resistor.
Todd